I'm a big fan of dual-core systems. I think there's a clear and substantial benefit for all computer users when there are two CPUs waiting to service requests, instead of just one. If nothing else, it lets you gracefully terminate an application that has gone haywire, consuming all available CPU time. It's like having a backup CPU in reserve, waiting to jump in and assist as necessary. But for most software, you hit a point of diminishing returns very rapidly after two cores. In Quad-Core Desktops and Diminishing Returns, I questioned how effectively today's software can really use even four CPU cores, much less the inevitable eight and sixteen CPU cores we'll see a few years from now.
To get a sense of what kind of performance improvement we can expect going from 2 to 4 CPU cores, let's focus on the Core 2 Duo E6600 and Core 2 Quad Q6600 processors. These 2.4 GHz CPUs are identical in every respect, except for the number of cores they bring to the table. In a recent review, Scott Wasson at the always-thorough Tech Report presented a slew of benchmarks that included both of these processors. Here's a quick visual summary of how much you can expect performance to improve when upgrading from 2 to 4 CPU cores
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